An air bag able to be rapidly expanded upon the occurrence of a collision of an automotive vehicle or the like to thus protect a passenger, is known. Conventionally, the rapid expansion of the air bag is caused by a high-speed discharge of a gas generated by burning a solid state gas generating material. As a typical solid state gas generating material, a material containing metallic azide generating a non-toxic nitrogen gas is used. The metallic azide produces a residual decomposition product and a large amount of reaction heat during the generation of the gas.
To properly activate the air bag upon a collision of the vehicle with an obstacle, it is necessary to produce an amount of approximately 30 to 100l of gas at a driver's seat and an amount of approximately 150 to 200l of gas for a passenger's seat, in a very short time, and accordingly, the inner pressure in an inflator should be at a high level, to thereby obtain a high speed burning of the gas generating material. This, however, requires that the thickness of a wall of a pressure vessel of the inflator be sufficient to withstand such a high pressure, and thus increases the weight of the inflator.
Various types and constructions of inflators have been disclosed in the prior art.
For example, an inflator 20 disclosed in U.S. Pat. No. 4,547,342, and shown in FIG. 1, comprises a pressure vessel 20 formed by welding an upper mirror plate 21 and a lower mirror plate 22, respectively having cylindrical portions 33 extending from the peripheral edges thereof, at the ends of these cylindrical portions 33. A cylindrical partitioning wall 23 is extended downward along an axis of the pressure vessel 20 from the upper mirror plate 21 in an inside of the pressure vessel 20, and at a position corresponding to the partitioning wall 23, a cylindrical partitioning wall 24 is extended upward from the lower mirror plate 22. The tip ends of the partitioning walls 23 and 24 are welded together to thereby define a gas generating chamber 26. The high pressure gas is generated within the gas generating chamber 26, and thus the partitioning walls 23 and 24 and the upper and lower mirror plates 21 and 22 have a wall thickness sufficient to withstand such a high pressure. Also, as shown in FIG. 1, a plurality of gas flow paths 27 are formed in the inflator through to the partitioning wall 24, and a plurality of through openings 32 are formed through the circumferential wall 33 of the pressure vessel 20, to thereby introduce the gas generated in the gas generating chamber 26 into an air bag body associated with the inflator.
A filter 28 formed by stacking a plurality of metallic nets is disposed inside of the partitioning walls 23 and 24 and extends between the upper and lower mirror plates 21 and 22. Also, a filter 29 similarly formed by stacking a plurality of metallic nets and extending between a deflector plate 35 projecting from the inner periphery of the lower mirror plate 22 and the upper mirror plate 21, is disposed outside of the partitioning walls 23 and 24. The filters 28 and 29, collect the residual decomposition product and cool the high temperature gas, upon a generation of the gas. In the drawings, reference numeral 30 denotes an ignition device and 34 denotes an ignition material, both disposed within a space defined by an upper central fixing portion 38 integrally formed with the upper mirror plate 21 and formed with a plurality of through holes 40 and a lower central fixing portion 37 integrally formed with the lower mirror plate 22. The upper and lower central fixing portions 38 and 37 are welded together at the joint therebetween. Reference numeral 31 denotes a gas generating material.
An air bag to be installed in a vehicle must be made as compact and light weight as possible, and accordingly, the air bag body and the inflator must be made as compact and light weight as possible.
A first possible method of reducing the weight of the inflator is to reduce the number of metallic nets forming the filters, but a reduction of the number of the metallic nets forming the filters, but a reduction of the number of the metallic nets inevitably causes a lowering of filtering effect for the residual decomposition product and allows a leakage of the solid state residual decomposition product into the air bag body, to thus damage the air bag body. In the worst case, a serious problem can occur due an injury suffered by a passenger from a discharge of the high pressure gas due to a rupture of the air bag body. Accordingly, a reduction of the inflator weight by reducing the number of the metallic nets cannot be considered practical. If an attempt is made to reduce the weight by reducing the thickness of the upper and lower mirror plates of the pressure vessel, the upper and lower mirror plates may be distorted by the high pressure thereon, and thus the gas will flow through portions other than the predetermined gas flow paths. When such flow of the gas through portions other those predetermined occurs, a problem arises of an insufficient filtering and gas cooling.
Various inflators other than that illustrated in FIG. 1 have been disclosed in the art.
For example, U.S. Pat. No. 4,131,299 discloses an inflator having a metallic fiber layer provided at the inside of the openings of the pressure vessel, but an inner cylinder corresponding to the partitioning wall of the above-discussed U.S. Pat. No. 4,131,299, must be provided in the pressure vessel, giving rise to problems similar to those set forth above.
Japanese Unexamined Patent Publication (Kokai) No. 55-110642 discloses an inflator having a separately formed cartridge disposed within the pressure vessel. The partitioning wall provided for this inflator has a construction similar to that in the above-discussed U.S. Pat. No. 4,131,299, and when a deformation of the upper vessel body occurs, a gap is formed between the partitioning wall and the upper vessel body, to allow a gas leakage therefrom. This leads to the problem that the leaked gas is externally discharged without filtering.
Japanese Examined Patent Publication (Kokoku) No. 62-5094 discloses an inflator in which the mirror plates have a curved plane, thus permitting thinner wall thickness of the pressure vessel, but such construction leads to the problem of an increase in the size of the inflator due to an external bulging of the curved planes.
Japanese Unexamined Patent Publication (Kokai) No. 2-155857 and U.S. Pat. No. 4,530,516 disclose an inflator in which the partitioning wall is formed by locally deforming the mirror plate. Even in these inflators, however, there is no teaching of a solution to the leakage of high pressure gas through portions other than the predetermined gas flow paths when the upper and lower mirror plates are expandingly deformed.
As described above, in the conventional inflator constructions, the actuation thereof cannot be assured with a reduced size and weight.